1. Field of the Invention
The present invention relates to a method for determining the flying height of a head of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
The disks are rotated by a spindle motor of the drive. Rotation of the disks creates an air flow within the disk drive. Each head has an air bearing surface that cooperates with the air flow to create an air bearing between the head and the adjacent disk surface. The air bearing eliminates or minimizes the mechanical wear between the head and the disk. The height of the air bearing is commonly referred to as the flying height of the head.
The magnetic field detected by the head is inversely proportional to the flying height of the head. Likewise, the strength of the magnetic field written onto the disk is also inversely proportional to the fly height. A larger fly height will produce a weaker magnetic field on the disk.
To determine head performance it is desirable to measure the flying height of a head. The flying height can be measured with an optical based test stand. In an optical flying height tester, a head “flies” adjacent to a rotating glass substrate. A light beam is directed through the substrate, reflects off of the head and is detected by a detector. The flying height is then computed based on the detected light.
There have been developed heads that include a heater coil. Current is provided to the heater coil to generate heat and thermally expand the head to vary the flying height. These types of heads are commonly referred to as fly on demand (“FOD”) heads. It is desirable to determine the flying heights of FOD heads to test and calibrate the drive. It is desirable to test FOD heads in the actual drive assembly. Optical based flying height testers can not be used to test the heads once assembled into the drive. For one thing, the substrates in the drive are not transparent to light. It would be desirable to provide a method to determine the flying height of FOD heads using the existing components of a hard disk drive.